#include <cstdio>
#include <iostream>
using namespace std;

int c, v0, v1, a, p, fns, vv, day;

int main() { 
    freopen("MrBA.in", "r", stdin);
    freopen("MrBA.out", "w", stdout);
    ios::sync_with_stdio(false);
    cin >> c >> v0 >> v1 >> a >> p;
    while(fns < c) { 
        vv = day * a + v0;
        if (vv > v1) vv = v1;
        if (day) { 
            if (fns > p) vv -= p;
            else vv -= fns;
        }
        fns += vv;
        day++;
    }
    cout << day << endl;
}

